Usually larger buildings will have an In-House maintenance department or even a house-keeping department, Call the main number and ask the receptionist to pass you thru to the person in charge of maintenance,
I have found that if you sound ****ed-off and are looking for somebody to rectify a problem then you get thru a little quicker, of course once you get thru its all sweetness and light:D

As stated earlier, by macroomboy, most companies of that size will in fact have some form of a maintenance department. Walking into an establishment like that can prove to be quite difficult. Usually you need an appointment, need to be signed in, visitor’s cards/escort etc. And most people in corporate settings don’t take to kindly to you just strolling in off the street without an appointment, though it can work on occasion. So it’s always best to get someone on the phone first. Just place a call, you’ll probably get a phone directory of some sort that can lead you to the right department or just go for the operator and ask for the facilities director. Any dealings with accounts of this size that I’ve had, the facilities director has always been the one to sign off on the work. Best of luck with it!